Screening of Traditional South African Leafy Vegetables for Specific Anti

a ISSN 0101-2061 Food Science and Technology DDOI http://dx.doi.org/10.1590/1678-457X.20416 Screening of traditional South African leafy vegetables for specific anti-nutritional factors before and after processing Humaira ESSACK1*, Bharti DDHAV1, John Jason MELLEM1 Abstract This study investigated the effect of processing on anti-nutritional factors of thirteen traditional leafy vegetables collected in Kwa Zulu-Natal, South Africa. The aim was to determine whether processing reduced anti-nutrient levels of leafy vegetables. The vegetables were boiled in a plant-to-distilled water ratio of 1:4 (w/v) at 97 °C for a time period of 5 and 15 min. The vegetables studied were: Amaranthus dubius, Amaranthus hybridus, Asystasia gangetica, Bidens pilosa, Ceratotheca triloba, Chenopodium album, Emex australis, Galinsoga parviflora, Guilleminea densa, Momordica balsamina, Oxygonum sinuatum, Physalis viscosa and Solanum nigrum. From this study, it was determined that non processed samples contained anti-nutrients such as tannins, phytic acid, alkaloids, oxalic acid, and cyanogenic glycoside. Both boiling parameters were effective in reducing the tannin, phytic acid, alkaloid, oxalic acid and cyanogenic glycoside contents of all 13 traditional leafy vegetables. The results of this study provide evidence that the local traditional leafy vegetables which the population is so reliant upon, are important contributors to micronutrient malnutrition in developing countries and can be minimized through common boiling methods for a minimum of 5 and maximum of 15 minutes. Keywords: traditional leafy vegetables; tannins; phytic acid; alkaloid; oxalic acid; cyanogenic glycoside. Practical Application: Minimization of anti-nutrients using boiling at different time periods. 1 Introduction Nutrition is of great importance especially when a plant or are low in micronutrients. Therefore, the daily micronutrient vegetable is being utilized as a source of food. It is imperative to requirements are obtained through traditional leafy vegetable note that endogenous toxic factors within the plant or vegetable consumption. Traditional leafy vegetables are inexpensive and can influence the nutrients present. These toxic factors are known easily accessible (Dmotoso, 2006). Traditional leafy vegetables as anti-nutrients. Anti-nutrients can be defined as chemicals are also easy to cook, provide roughage and are rich in vitamins which are present within the plant to protect the plant as a and minerals (Lin et al., 2011). Traditional leafy vegetables defence mechanism and aid in other biological functions. They grow wildly, do not require formal cultivation and can provide reduce the ability of nutrients such as minerals, vitamins and high nutrition for poor communities where malnutrition is even proteins within the plant material. This, in turn, affects rife (World Health Drganization, 1982). A summary of the the nutritional value of these plants. Anti-nutrients comprise of traditional leafy vegetables used in the study are depicted in amino acids to proteins, simple amines to alkaloids, glycosides Table 1 (Hutchings et al., 1996). Traditional leafy vegetables are and phenolic compounds. When a plant food is consumed as a plentiful in South Africa and are known to contain anti-nutrients nutritional source, along with this, anti-nutrients are consumed such as glycosides, oxalic acid, alkaloids and hydrocyanic acid. and pose a health risk to the consumer (Ugwu & Dranye, 2006). The presence of anti-nutrients indicates that the evaluation of In sub-Saharan Africa, most of the population live in rural anti-nutritional factors is therefore necessary (Hutchings et al., regions. The World Health Drganization (WHD) have stated that 1996). Many workers, (Ddhav et al., 2007) have reported the chronic nutrition deficiency affects 200 million of the sub-Saharan nutritive value of traditional leafy vegetables, however, the population, which is equivalent to 42% of the population. anti-nutritive values have not been explored. The sub-Saharan population is known to have a prevalence in Tannins are identified as plant polyphenols that are capable disease. This could be attributed to many factors such as diet of forming complexes with metals ions and macro-molecules changes or environmental factors. Based on FAD reports, about like proteins and polysaccharides. Tannins affect the nutritional 1 billion people especially in developing countries depend on value of food products by chelating metals like iron and zinc and edible wild plants in their diets. Some of these plants are not reducing the absorption of these nutrients as well as forming only edible, but also have medicinal uses (Unuofin et al., 2017). complexes with protein thereby inhibiting their digestion and Due to inaccessibility of resources, the population’s nutrition, is absorption (Dlawoye et al., 2017). Tannins are responsible for sourced from local cereals and plant foods. The staple food in a protein deficiency syndrome known in Sub-Saharan Africa as sub-Saharan Africa is based on a diet containing cereals, which Received 11 Aug., 2016 Accepted 30 Apr., 2017 1 Department of Biotechnology and Food Technology, Faculty of Applied Sciences, Durban University of Technology, Steve Biko Campus, Durban, South Africa *Corresponding author: [email protected] 462 Food Sci. Technol, Campinas, 37(3): 462-471, July-Sept. 2017 Essack; Ddhav; Mellem ‘Kwashiorkor’. Tannins are responsible for a decrease in growth of macro and micro nutrient malnutrition amongst developing rate as well as a non-palatable taste. Phytic acid is the major countries the need for anti-nutrient testing and ways to reduce phosphorous storage compound in traditional leafy vegetables. them is in great demand. Phytic acid has been recorded to inhibit the absorption of Different processing techniques are often utilized in order to minerals and reduce the bioavailability of metal ions like zinc reduce anti-nutritional factors (Embaby, 2010). Some processing and iron as well as affect protein and starch digestion. A phytic techniques are performed on household level or domestically and acid intake of 4-9 mg/100g decreases iron absorption in humans others are performed on a larger scale in industry (Raes et al., by 4-5 fold. Too much of a phytate rich diet is associated with 2014). Cooking is a common form of processing in plants that nutritional diseases such as rickets and osteomalacia in children are consumed as a food source. Cooking causes changes in the and adults (Unuofin et al., 2017). Alkaloids are basic nitrogenous phytochemistry of the traditional leafy vegetable affecting its compounds produced as metabolites that cause biological effects bioaccessability and health benefit properties. The degree of based on consumption. They occur quite often as a mixture these changes depend largely on the cooking methods as well of compounds of related structure. They are found in about as the traditional leafy vegetable (Ddhav et al., 2007). 15-20% of vascular plants, in seeds, leaves, roots, bark etc. They are classified into three groups. True alkaloids (e.g. Pyridine), The proposed research initiative was to conduct a preliminary are heterocyclic nitrogenous bases derived from amino acids assessment of the anti-nutritional factors from an array of selected toxic to humans and animals, e.g. tobacco and nicotine. Pseudo indigenous and underutilized South African traditional leafy alkaloids (e.g. Purine alkaloids), are heterocyclic nitrogenous vegetables and the effective processing time to minimize these bases and their precursors are not amino acids. They are less anti-nutritional factors with a view to promote their utilization toxic than true alkaloids, e.g. caffeine in coffee. Protoalkaloids and contribute to the socio-economic development of the people are basic amines derived from amino acids but the nitrogen is living in areas where these plants are found. not heterocyclic, e.g. capsaicin in hot peppers. A consumption of high tropane alkaloids can cause rapid heartbeat, paralysis and 2 Materials and methods in fatal cases, death (Velisek, 2014). Dther toxic action includes disruption of the cell membrane in the gastrointestinal tract 2.1 Sample collection and preparation (Unuofin et al., 2017). Dxalic acid exists in many leafy vegetables Anti-nutritional analyses (tannins, phytic acid, oxalic acid, and plant foods. Depending on species, oxalic acid can occur alkaloids and cyanogenic glycoside) were conducted using as soluble salts of potassium and sodium or as insoluble salts of the raw leaves and boiled leaves of thirteen traditional leafy calcium, magnesium or iron or it can occur as a combination vegetables. Table 1 indicates a brief overview of the traditional of soluble and insoluble salts. This forms strong chelates with leafy vegetables used in the study. The plants were identified and dietary calcium inhibiting its absorption. (Akwaowo et al., sourced from general farm land during the months of January 2000). It’s well known that oxalic acid and its salts can have a to March in Durban, Kwa-Zulu Natal, South Africa. Voucher deleterious effect on human nutrition and health, mostly by specimens were housed in Ward Herbarium, University of decreasing calcium absorption and aiding the formation of Kwa-Zulu Natal, Durban, South Africa. Biodata on the plants kidney stones (Dlawoye et al., 2017). are listed in Table 1 (Hutchings et al., 1996). The leaves were There are many traditional leafy vegetables which are known carefully inspected and damaged or infected

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